They describe society as a human superorganism and that what we feel, think, do or say, can spread to others, including those we don’t know.

The implications for brands are startling given the old adage that word of mouth is the best form of advertising. It’s commonly believed that word of mouth relies on trust of the source – but could it be their thoughts and behaviors are contagious as well?

The researchers say that while it’s not clear how contagions spread they think some may be passed on subconsciously and a range of human ailments can be caught this way including acne, smoking and headaches, according to Fowler and Christakis.

When we see a fat person, they say, it resets our perception of what a normal person should look like and as a result allows us to become fat, and this can radiate to three degrees of separation.

Other scientists however are not convinced. Russell Lyons, a mathematician at Indiana University, says there’s no proof obesity can be contracted at distance; the proximity of a fastfood outlet is more likely to be a factor.

While the jury is out, the success of Connected, which has landed a spot on Oprah’s must read list, is evidence that something is contagious, probably word of mouth!